Low inductance, ferrite sub-gap substrate structure for surface film magnetic recording heads

ABSTRACT

A thin film magnetic recording head is fabricated by forming a substrate from opposing ferrite blocks which have a ceramic member bonded between them. This structure is then diced to form a plurality of columns, wherein each column has a ferrite/ceramic combination. Each column represents a single channel in the completed head. A block of ceramic is then cut to match the columned structure and the two are bonded together. The bonded structure is then cut or ground until a head is formed, having ceramic disposed between each channel. A ferrite back-gap is then added to each channel, minimizing the reluctance of the flux path. The thin film is patterned on the head to optimize various channel configurations.

This application is a continuation of application Ser. No. 09/475,420,filed on Dec. 30, 1999, which is hereby incorporated in its entirety byreference.

FIELD OF THE INVENTION

This invention relates generally to magnetic recording heads and moreparticularly to a structure for a ferrite driven, surface thin-filmmagnetic recording head wherein a substantial portion of the ferritecore has been replaced with a magnetically impermeable material and anoptimal back-bar arrangement which reduces the inductance and increasesthe efficiency of the head.

BACKGROUND OF THE INVENTION

While a variety of data storage mediums are available, magnetic taperemains a preferred forum for economically storing large amounts ofdata. In order to facilitate the efficient use of this media, magnetictape will have a plurality of data tracks extending in a transducingdirection of the tape. Once data is recorded onto the tape, one or moredata read heads will read the data from those tracks as the tapeadvances, in the transducing direction, over the read head. It isgenerally not feasible to provide a separate read head for each datatrack, therefore, the read head(s) must move across the width of thetape (in a translating direction), and center themselves over individualdata tracks. This translational movement must occur rapidly andaccurately.

In order to facilitate the controlled movement of a read head across thewidth of the media, a servo control system is generally implemented. Theservo control system consists of a dedicated servo track embedded in themagnetic media and a corresponding servo read head (which is usually oneof the standard read heads, temporarily tasked to servo functions) whichcorrelates the movement of the data read heads.

The servo track contains data, which when read by the servo read head isindicative of the relative position of the servo read head with respectto the magnetic media in a translating direction. In one type oftraditional amplitude based servo arrangement, the servo track wasdivided in half. Data was recorded in each half track, at differentfrequencies. The servo read head was approximately as wide as the widthof a single half track. Therefore, the servo read head could determineits relative position by moving in a translating direction across thetwo half tracks. The relative strength of a particular frequency ofservo signal would indicate how much of the servo read head was locatedwithin that particular half track. The trend toward thinner and thinnermagnetic tape layers causes amplitude modulation problems with this andother amplitude based heads. That is, as the thickness of the magneticlayer decreases, normal variations on the surface represent a muchlarger percentage variation in the magnetic layer, which willdramatically affect the output signal.

Recently, a new type of servo control system was created which allowsfor a more reliable positional determination by reducing the amplitudebased servo signal error traditionally generated by debris accumulation,media thickness non-uniformity and head wear. U.S. Pat. No. 5,689,384,issued to Albrecht et al. on Nov. 19, 1997, introduces the concept of atiming based servo pattern on a magnetic recording head.

In a timing based servo pattern, magnetic marks (transitions) arerecorded in pairs within the servo track. Each mark of the pair will beangularly offset from the other. For example, a diamond pattern has beensuggested and employed with great success. The diamond will extendacross the servo track in the translating direction. As the tapeadvances, the servo read head will detect a signal or pulse generated bythe first edge of the first mark. Then, as the head passes over thesecond edge of the first mark, a signal of opposite polarity will begenerated. Now, as the tape progresses no signal is generated until thefirst edge of the second mark is reached. Once again, as the head passesthe second edge of the second mark, a pulse of opposite polarity will begenerated. This pattern is repeated indefinitely along the length of theservo track. Therefore, after the head has passed the second edge of thesecond mark, it will eventually arrive at another pair of marks. At thispoint, the time it took to move from the first mark to the second markis recorded. Additionally, the time it took to move from the first mark(of the first pair) to the first mark of the second pair is similarlyrecorded.

By comparing these two time components, a ratio is determined. Thisratio will be indicative of the position of the read head within theservo track, in the translating direction. As the read head moves in thetranslating direction, this ratio will vary continuously because of theangular offset of the marks. It should be noted that the servo read headis relatively small compared to the width of the servo track. Ideally,the servo head will also be smaller than one half the width of a writtendata track. Because position is determined by analyzing a ratio of twotime/distance measurements, taken relatively close together, the systemis able to provide accurate positional data, independent of the speed(or variance in speed) of the media.

Of course, once the position of the servo read head is accuratelydetermined, the position of the various data read heads can becontrolled and adjusted with a similar degree of accuracy on the samesubstrate. Namely, the various read heads are fabricated on the samesubstrate with a known spacing between them. Hence knowing the locationof one allows for a determination of the location of the remainder ofthe read heads.

When producing magnetic tape (or any other magnetic media) the servotrack is generally written by the manufacturer. This results in a moreconsistent and continuous servo track, over time. To write the timingbased servo track described above, a magnetic recording head bearing theparticular angular pattern as its gap structure, must be utilized. As itis advantageous to minimize the amount of tape that is dedicated toservo tracks, to allow for increased data storage, and it is necessaryto write a very accurate pattern, a very small and very precise servorecording head element must be fabricated.

Two types of servo recording heads having a timing based pattern areknown. The first is a pure thin film head, such as that disclosed byAboaf et al. in U.S. Pat. No. 5,572,392, issued on Nov. 5, 1996. With apure thin film head, all of the components of the head are created fromlayering different materials, as thin films, on an inert substrate. Forexample, the magnetic core, the windings and any barrier materials areformed by producing thin films. Such a head has very low inductance,however, it is extremely difficult to manufacture. To date, pure thinfilm heads are generally not utilized for time based servo heads and arenot seen as a practical way to produce such a magnetic head.

A very different type of recording head is taught by Albrecht et al. inthe '384 patent. This second type of head is referred to herein as asurface film or surface thin film head and is illustrated as 100, inFIG. 18. The surface film head 100 includes two C-shaped ferrite blocks110, 112 that are bonded to a ceramic member 114 that extends the entirewidth of the head 100. A surface is then polished flat or contoured andprepared for this film deposition. A magnetically permeable thin film116 is deposited over an upper surface of the ferrite blocks 110, 112and the exposed upper portion of the ceramic member 114. The thin film116 is shown much larger than it would actually be, respective to theother elements. Gaps 118 are formed in the thin film 116, in anappropriate timing based pattern. Windings 120 are wrapped and areelectrically driven to drive flux around the ferrite core and throughthe thin film 116 (in the direction of arrow A). The flux leaks from thegaps 118 and writes media passing over it.

Such a surface film head has a high inductance due to the large volumeof ferrite forming the core and a high reluctance “back-gap”, due to theseparation of the ferrite block 110, 112 by the ceramic member 114, onthe underside of the head (i.e., opposite the thin film 116). The sizeand dimensions of the head are determined by the end usecharacteristics. For example, the width of the head 100 is defined bythe width of the media; i.e., a head that is 19 mm wide is appropriateto support a tape that is 12.5 mm wide. The ceramic member 114 must bethick enough to allow the proper patterns 118 to be located above it andis approximately 0.012″ in the known versions of the Albrecht et al.head, produced by IBM. The length of the head must be sufficient tosupport the media as it travels over the tape bearing surface and thedepth (especially of the ferrite cores) must be sufficient to allowappropriate windings to be attached and to allow the head to be securelyfixed in a head mount.

With the surface film head, flux is forced to travel through amagnetically permeable thin film that bridges a generally magneticallyimpermeable barrier between sections of the core. The writing gap islocated within this thin film and the magnetic flux is expected to leakfrom this gap and write the media. The width of the ferrite is muchlarger than the sum of the channel widths. Hence, there is a largeamount of unnecessary ferrite inductance. In other words, as a result ofthe relatively large amount of extraneous ferrite, an unnecessarily highamount of inductance is created. Therefore, to produce a relativelysmall amount of flux leakage through a small gap in the thin film, veryhigh levels of current are required to generate sufficient magnetic fluxthroughout the relatively large core. This requires greater writecurrent from the drive circuitry, lowers the frequency response of thehead, and increases the rise time of the writing pulses from the head.

The thin film layer bridges a “gap” between the ferrite sections of thesubstrate, at one end of the head. This is, of course, the writing endof the head. This gap, referred to as the “sub-gap” by the presentinventor to distinguish it from the writing gaps in the thin film, isformed from and defined by the ceramic insert. As discussed above, theceramic insert extends through the entire height of the write head. Thisforms a very large “back-gap” in a portion of the head opposite the thinfilm layer. This back-gap, in some prior recording heads, is a portionof the head where the magnetic flux must travel through the ceramicmember in order to complete the magnetic circuit. Ultimately, this formsa barrier which hampers the magnetic flux; in other words the reluctancethrough the back-gap is relatively high and again, the head must bedriven harder to compensate. This is only really problematic in headshaving a larger back-gap with respect to the writing gap, such as inAlbrecht et al. Various other magnetic heads, video for example, willhave a back-gap length equal to the writing gap length. In addition, thevideo core back-gap is made very tall, thus increasing its area andreducing the back-reluctance. Techniques used to reduce the reluctanceof video recording heads are not applicable to sub-gap driven heads.

Such problems are intensified with heads having multiple writing gaps,or channels. As shown in FIG. 18, a single core is driven andsimultaneously writes multiple channels (each of the writing gaps 118forms a separate channel). In order to do so, a multi-channel head willnecessarily have to be wider than a single channel head. This in turnnecessitates that the core become larger. All of this leads to a headhaving a larger amount of magnetically permeable material through whicha predetermined amount of magnetic flux must flow while attempting toconsistently and simultaneously write multiple channels. In other words,excess and unused ferrite material is provided in between the channelswhich unnecessarily increases the overall inductance of the head.

Therefore, there exists a need to provide an efficient multi-channeltiming based head having a lower overall inductance, a lower reluctancethrough the back-gap, a higher frequency response, and greaterefficiency. Furthermore, there exists a need to provide such amulti-channel head with the ability to individually and separately driveand control each channel.

SUMMARY OF THE INVENTION

The present invention relates to a low inductance, high efficiencysub-gap, surface thin film magnetic recording head and a method offabricating the same.

A substrate consisting of a ceramic member, glass bonded between a pairof ferrite blocks is prepared. After the substrate is created, it isdiced to form a base from which a plurality of columns extend. Thenumber of columns will correspond to the eventual number of channels ina completed recording head. A ceramic block is prepared whichcorresponds to the dimensions of the substrate. Channels or notches arecut into the ceramic block so that the substrate columns engage them ina male/female relationship. The channels allow for the entirety of thecolumn to be accepted within the channel so that the base of thesubstrate flushly abuts the corresponding base of the ceramic block. Theceramic block is then adhered to the substrate. In particular, thecolumns of the substrate are glass bonded to the interior of thechannels in the ceramic block, thus forming a head member.

The top and bottom of the head member are then cut or ground to producea uniform block of alternating ceramic portions and substrate columnswherein each substrate column includes a sub-gap. A sufficient amount ofthe head member is cut or ground so that the substrate columns extendthrough the entire height of the remaining portion of the head member.During this process, the upper portion of the head member can beappropriately radiused, as it is this section which will become the tapebearing surface of the writing head.

If desired, air bleed slots can be cut into the head member,perpendicular to the direction of tape travel. On top of the headmember, a magnetically permeable thin film is deposited, preferably by asputtering process. It is within this thin film that the writing gapswill be produced. As such, any known process of forming these gaps inthe thin film is acceptable. To the extent that various platingtechniques will be utilized, those gaps would be formed accordingly.

At this point, a back-bar is attached to the head member. The back-baris formed from an appropriate magnetically permeable material, such asferrite. The back-bar is provided with a structure so that it may bewrapped with an appropriate winding to produce a coil. The back-bar canbe formed in a wide variety of configurations. In the simplest form, asingle winding is provided around all of the back-bars, and when driven,will engage each of the channels simultaneously. Alternatively, aseparate winding is provided for each channel, thus allowing eachchannel to be separately driven and controlled. Furthermore, anyintermediary combination is allowable. That is, any particularcombination of channels can be tied together. When the channels aretimed and driven independently, sections of the magnetically permeablethin film must be removed between the channels. This prevents magneticflux from passing from one channel to another through the thin filmlayer. It is the prevention of this cross talk which allows themulti-channel head to have its channels driven independently in time orphase. To produce such isolation, sections of the thin film can beremoved by ion milling, wet chemical etching, or by any other knownprocess. Other techniques such as selective plating or selectivespattering could also be used.

In one embodiment, the present recording head provides a magneticallyimpermeable barrier between each channel so that actuation of onechannel will in no way interfere with any other channel in the head.Hence, a significant portion of the magnetic volume of the head layingbetween each channel has been replaced with a ceramic material.Furthermore, in the back-gap area a back-bar has been incorporated.Utilization of the back-bar serves to reduce the reluctance of theback-gap and increase the efficiency of the head. Due to the reductionin overall volume of the ferrite core in the interchannel area, the headhas a lower total inductance and is therefore more easily driven. Due tothe lower inductance per channel, the frequency response of the head canbe greatly increased. This increased response time translates intofaster current rise times for the output flux signal generated. Thisultimately leads to sharper written transitions when the head is used toapply servo patterns to magnetic media. It also allows for specificpatterns to be accurately and quickly written by individuallycontrolling and driving the various channels of the head.

In another aspect of the present invention, the magnetically permeablethin film layer is optimally configured to complete a magnetic circuitfor each channel, while limiting mechanical interference of the filmwith the air bleed slots. Consideration must be given to the minimalrequirements for completing the circuit and the engagement of the mediaagainst a head having a non-planar surface while minimizing thecomplexity of providing the air bleed slots. In addition, when workingwith components of this scale, consideration must be given to theetching or milling technique utilized to impart and define the thin filmlayer so that mechanical shear or peeling of the film is not induced bythe tape's motion.

It is an object of the present invention to provide a multi-channelmagnetic surface film servo write head having a reduced volume ofmagnetically permeable material.

It is a further object of the present invention to reduce the reluctanceof the back-gap portion of the magnetic recording head.

It is another object of the present invention to provide a magneticrecording head having multiple channels wherein each channel isseparately and individually controllable.

It is still another object of the present invention to provide a methodof making a multi-channel head wherein each channel is isolated from thenext.

It is yet another object of the invention to provide a highly efficientmulti-channel recording head having a relatively high frequency responsesuitable for use as a servo write head.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side planar view of a substrate composed of ferrite blocksglass bonded to a ceramic member.

FIG. 2 is a top planar view of the substrate shown in FIG. 1.

FIG. 3 is a side view of the substrate of FIG. 1, diced into a pluralityof columns.

FIG. 4 is a side view of a ceramic block having a plurality of notches.

FIG. 5 is a side view of the ceramic block and the substrate bondedtogether.

FIG. 6 is a top view of the bonded substrate after the top and bottomhave been cut or ground.

FIG. 7 is a side view of the bonded substrate after the top and bottomhave been cut or ground.

FIG. 8 is a top view of a head assembly.

FIG. 9 is a side view of a head assembly.

FIG. 10 is an end sectional view taken about line 10-10.

FIG. 11 is an end sectional view taken about line 10-10 and having aback-gap attached.

FIG. 12 is a side view of a head assembly having a plurality ofback-bars affixed thereto, with coils individually wrapped about eachback-bars.

FIG. 13 is a side view of a head assembly having a plurality ofback-bars affixed thereto, with a single coil wrapped about all of theback-gaps.

FIG. 14 is a head assembly showing a pattern of thin film.

FIG. 15 is a head assembly showing various patterns of thin film.

FIG. 16 is a head assembly showing various patterns of thin film.

FIG. 17 is a head assembly showing various patterns of thin film.

FIG. 18 is a perspective view in a prior art surface thin film magneticrecording head.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is a multi-channel head and method of making thesame. Referring to FIG. 1, a substrate 10 is created by glass bondingtwo C-shaped ferrite blocks 12 to a medially disposed ceramic member 14.The sizes, shapes and relative proportions of the ferrite blocks 12 andceramic member 14 may vary as dictated by the desired parameters of thecompleted recording head. Furthermore, the choice of materials may alsovary so long as blocks 12 remain magnetically permeable while member 14remains substantially magnetically impermeable. FIG. 2 is a top view ofthe substrate 10.

Referring to FIG. 3, substrate 10 is diced so as to form a plurality ofcolumns 16A-16E which remain adhered to base 18. Columns 16A-16E arealso shown by the dashed lines in FIG. 2, which illustrates how eachcolumn will have a ceramic portion (sub-gap) bonded between two ferritepoles. The dashed lines are merely illustrative of future columns, asthe substrate 10 in FIG. 2 has yet to be diced. As shown is FIG. 4, aceramic block 20, or slider, is cut to form a plurality of channels ornotches 22A-22E. The ceramic block 20 can be formed from bariumtitanate, or any other suitable magnetically impermeable material. Thenotches 22A-22E are cut to correspond with columns 16A-16E. As such, therelative size and shape of the columns 16A-16E and the notches 22A-22Eshould correspond; beyond that the selection of size and shape willsimply depend on the desired final parameters of the completed magnetichead.

As illustrated in FIG. 5, substrate 10 is mated with ceramic block 20.More specifically, columns 16A-16E are inserted into notches 22A-22Euntil the upper surface 26 of the base 18 of substrate 10 flushly meetsthe lower surface 28 of ceramic block 20. Subsequently, substrate 10 isadhered to ceramic block 20. This can be accomplished in any known way.In its most preferred form, substrate 10 is glass bonded to ceramicblock 20. To accomplish this, the substrate 10 is clamped or otherwisesecured to ceramic block 20, as shown in FIG. 5. Glass rods are placedinto the various notches 22A-22E, in a space left by the columns16A-16E. The assembly is then heated to a temperature sufficient to meltthe glass rods. This causes the melted glass to wick along the abuttingsides of the columns 16A-16E and the notches 22A-22E. Once allowed tocool, the glass hardens and bonds the members together.

The top and the bottom of this assembly are then cut or ground away toarrive at the head substrate 30 shown in FIGS. 6 and 7. From a top viewand moving left to right (as illustrated), head substrate 30 has aceramic portion 32A, which is a remainder of ceramic block 20. A bead ofglass 33 bonds ceramic portion 32A to ferrite column 16A. Mediallydissecting ferrite column 16A is a portion of ceramic member 14, whichis likewise glass bonded to ceramic portion 32A. It is to be understoodthat the portion of the non-magnetic ceramic member 14 extends throughthe entire length of the remaining ferrite column 16A, thus dividing itinto two magnetic poles. Glass bonds 33 likewise join ceramic portion32B between ferrite columns 16A and 16B. This pattern is repeated acrossthe head, with the number of ferrite columns 16A-16E, representing theeventual number of channels in the completed write head. FIG. 7 is aside view of head substrate 30 and illustrates that the ferrite columns16A-16E (with included sections of ceramic member 14, not visible inthis view) forming a sandwich pattern with the ceramic portions 32A-32F.As illustrated (in FIG. 4), the notches 22A-22E extend through theentire width of the ceramic block 20. Thus, the ferrite columns 16A-16Eare visible from a side view (FIG. 7).

Head substrate 30 is now ready to be formed into a completed magneticrecording head. To summarize the remainder of the fabrication, a slightradius or curvature is caused on the upper surface of the head substrate30. This step could occur when removing the top section from the bondedsubstrate 10 and ceramic block 20, or it could be done at this stage asa separate operation. The curvature is imparted to the head substrate 30because its uppersurface will become the tape bearing surface of thecompleted head. This curvature facilitates smooth contact with the mediaunder tension. A magnetically permeable thin film layer 34 is depositedacross the upper surface of the head substrate 30. Writing gaps 36 (FIG.8) are caused to be formed in this thin film 34, aligned with thevisible portion of ceramic member 14, or in other words, above thesub-gap. Alternatively, the head contour could be finished into agenerally flat surface having integrated negative pressure channels. Theuse of these various contours is known in the art.

Either prior to depositing the thin film or after, air bleed slots 38may be cut into head substrate 30 along the tape bearing surface as isknown in the art. Once head substrate 30 has been fabricated into arecording head, magnetic tape will move across its upper surface in atransducing direction. Therefore, the air bleed slots 38 are cutperpendicular to the transducing direction. As the tape moves over therecording head at relatively high speed, air entrainment occurs. Thatis, air is trapped between the lower surface of the tape and the uppersurface of the recording head. As the tape moves over the recordinghead, the first air bleed slot encountered serves to skive off thetrapped air. The second and subsequent slots continue this effect, thusserving to allow the tape to closely contact the recording head. As thetape passes over the recording gaps 36, it is also held in place by theother air bleed slots 38 encountered on the opposite side of the gaps30.

FIG. 10 is an end, partially sectional view of head substrate 30 takenabout line 10-10. This figure illustrates the relationship between theferrite column 16A and the remaining portion of ceramic member 14. Thinfilm layer 34 is located on its upper surface and write gaps 36 arelocated immediately above the portion of ceramic member 14. Air bleedslots 38 are located on opposite side of ceramic member 14 and traversethe whole assembly. FIG. 11 illustrates the back-bar 40 of the presentinvention as it is attached to ferrite column 16A (again an end,partially sectional view taken about line 10-10). Back-bar 40 is asubstantially U-shaped ferrite block which is caused to abut each sideof the ferrite column 16A. The shape is chosen to efficiently complete amagnetic circuit and allows a coil 44 to be wound. The back-bar 40flushly abuts column 16A at is held in place by a bonding agent that isapplied at glue points 42. The use of back-bars 40 is advantageous inand of itself. In other words, using the back-bar 40 of the presentinvention will allow a better surface film head to be producedirrespective of the number of channels formed, or whether the combedstructure is utilized to achieve channel separation or to lower strayinductance by reducing the volume of magnetically permeable material inthe core.

Reluctance is proportional to the length and inversely proportional tothe area of the barrier. In the prior art surface film recording head(Albrecht et al.), the barrier in the back-gap is defined by the ceramicmember 14. The area in question will be defined by the area of contactbetween the ferrite blocks 110, 112 (FIG. 18) and the ceramic member114. Length corresponds to the thickness of the ceramic member 114. Thethickness of the ceramic member 114, is necessitated by the spatialrequirements of the writing gaps 36, and in other words cannot bereduced. In the present invention (FIG. 11) back-bar 40 has been added.The ceramic member 14 has been removed (effectively bypassed) as a fluxbarrier, but replaced with two much smaller air gap barriers where theback-bar 40 abuts the ferrite column 16A. Again, the barrier in questionwill be defined by the amount of contact, which is in turn defined bythe parameters chosen for the ferrite block 12 (as the back-bar 40 ischosen to correspond). However, the length involved is minuscule as itis defined by the “air gap” created by the abutment of two substantiallyplanar surfaces. As such, the total amount of reluctance in the presentback-bar 40 is a very small fraction of the total reluctance in priorart surface film recording heads. This leads to the fabrication of ahighly efficient magnetic recording head, as the reluctance of the corehas been significantly reduced.

By using the columned or combed structure, the volume of unnecessary ornon-useful magnetically permeable materials is greatly reduced, thusdecreasing the overall inductance of the head. As such, the frequencyresponse is dramatically increased, thus allowing faster and moreaccurate writing of data on the media. This is possible because theinducement of sufficient magnetic flux requires substantially lessenergy input. As such, the rise time of the written pulse issubstantially shortened. Thus allowing for a sharper written transitionin the media.

The above description relates to the general fabrication of a highlyefficient surface thin film magnetic recording head according to theteachings of the present invention. That is, by using the columned (orcombed) structure for the body of the head which reduces the overallinductance of the head, and by applying back-bars 40 which reduces thereluctance, an improved head is necessarily formed. In addition thereare various other parameters which can be modified to apply the head ofthe present invention to a wide variety of writing functions. It shouldbe noted that simply using a combed or columned structure in and ofitself produces a better, more efficient head. Likewise, the use ofback-bars 40 is also independently advantageous and can be utilized onheads having a combed or non-combed core, as efficiency will beincreased in both cases.

Referring to FIGS. 12 and 13, two substantially completed heads 46 areshown. In FIG. 12, head 46 is a multi-channel head having fiveindependent channels. That is, each channel can be individuallytriggered and caused to write, independent of the other four channels.To accomplish this, each back-bar 40 has its own coil 44 wrapped aboutit. In a variety of known ways, these coils 44 can be coupled to acontroller and appropriately driven. In FIG. 13, the back-gaps 40 areconfigured in the same way, however a single coil 44 is coupled to allof the back-gaps 40. In this way, when the coil is energized, thevarious channels will each write simultaneously. Any intermediatecombination is likewise achievable. That is, the individually wrappedcoils 44 (FIG. 12) can be tied together, achieving the same result asutilizing a single coil 44. Alternatively, any number or combination ofchannels can be coupled mechanically or electrically together.

In the preferred embodiment, each back-bar 40 is sized to correspond toan individual channel. As discussed, these back-bars 40 can then beseparately wound or wound as a single unit. In addition, a singleelongate back-bar 40 could be provided that extends along the entirelength of the recording head 46. For example, as shown in FIG. 11,back-bar 40 would extend into the page along the entire length of thehead.

An additional advantage of separately driving each channel individually,is the ability to fine tune each channel. As is known in the art and isgenerally represented by an “I-Sat” curve, each head and moreparticularly each channel will saturate at different levels of currentinput (respective to the number of turns in the coil). Therefore, it isdesirable to select a particular level of current input to maximize theefficiency and output of each channel. This optimal value often variesfrom channel to channel. As such, by performing this evaluation for eachchannel, the optimal current input for each channel can be determined.This information is moot in those heads where all the channels aredriven by a single coil. However, with independently driven channels,each channel is driven at its optimal level of current input(ampere-turns).

The head 46 of the present invention has been shown to have fivechannels. Any number of servo channels could be so fabricated. Fivechannel or two channel heads seem to be an industry standard for themoment. As the number of servo channels increases, the width of eachchannel must become narrower in order to prevent excessive depletion ofthe space available for data.

The choice to produce a multi-channel head having independent channelsor one having its channels tied together also affects the application ofthe thin film 34 to the tape bearing surface of the head 46. Morespecifically, a multi-channel head having independently driven channelsmay need to have those channels magnetically isolated from one anotherto avoid cross talk, depending upon the timing of the information beingwritten.

When cross-talk is not an issue, the surface thin film layer 34 canextend across the entire surface of the head, producing a unitary sheetfilm. However, the areas of sheet film between the channels may not bewell saturated, due to the limited width of the channels and hence thedriven core(s), in relation to the overall area of the sheet film. Thus,the areas of sheet film between adjacent channels may provide anundesirable high permeable flux leakage path which limits the amount ofsignal flux actually passing across the writing gaps 36. Hence, evenwhen cross-talk is not an issue, the preferred embodiment of the lowinductance, multi-channel timing based servo head of the presentinvention will include a separate thin film layer 34 that is dedicatedto a single channel and is magnetically isolated from the adjacentchannels. The process of providing channel separated thin film 34 areasis discussed below.

In addition, the application of the thin film 34 affects the creation ofthe air bleed slots 38. Namely, if the slots 38 are cut into the head 46after the thin film 34 has been deposited, rough corners may be producedwhich negatively affects the interaction between the head 46 and themedia. If the thin film 34 is deposited after the slots are cut, thinfilm step coverage over the slots becomes yet another issue.

The present invention contemplates a variety of techniques to deal withthe above mentioned considerations. The particular technique selectedwill also depend on the method used to form the writing gaps 36 into thethin film layer 34.

FIG. 14 represents the simplest head fabrication format. Here, head 46is a multi-channel head wherein the various channels are all coupledtogether. Though not shown, the gaps 36 will be patterned into eachchannel above the ceramic member 14 (i.e., that of FIG. 13). Assuming astaggered pattern is desired, the various gaps 36 would be so arranged.Thin film layer 34 (designated by the hash lines) has been depositedover the entire surface of head 46. As discussed above, this makes thecutting of air bleed slots 38 problematic. However, this problem can bereduced by slitting the heads prior to applying the film. As such, arelatively high quality head 46 can be produced. The advantage of suchan arrangement is that the thin film layer 34 provides a uniform tapebearing surface over the entirety of the upper surface of head 46.Conversely, the photolithography becomes more difficult due to theslots.

FIG. 15 represents a modified embodiment of a multi-channel head whereinthe channels are all coupled together. Once again, cross talk betweenchannels is not an issue. Here, thin film layer 34 is contained betweenupper and lower bounds defined by air bleed slots 38. This arrangementavoids the above discussed issue of cutting through the thin film layer34 or depositing the thin film layer 34 over existing air bleed slots38. The production of this thin film 34 pattern can be accomplished invarious ways. For example, prior to creating air bleed slots 38, a thinfilm 34 could be deposited over the entire upper surface of head 46.Then, areas of that thin film could be removed; leaving only the areadesignated in FIG. 15. This deposition could be selectively defined by aselective plating or a selective sputtering process used with theappropriate masks, or the film could be selectively removed afterdeposition, using any known technique.

Turning to FIG. 16, thin film layer 34 can also be configured for usewith independently driven channels in a multi-channel head. In order tobe operable, each channel must be magnetically isolated from itsadjoining channels. Primarily, this accomplished by ceramic sections32A-32E. However, if thin film layer 34 were continuous from one channelto the next, cross talk would occur, thus eliminating the ability toindependently control the channels. As such, with any independentlydriven, multi-channel head 46, the magnetically permeable thin filmlayer 34 must be absent between the various channels. The pattern 48 ofthin film 34 (covering channels 1 and 2) in FIG. 16, illustrates thesimplest way of accomplishing this. A strip 50 is devoid of the thinfilm 34, over the entire length of the head. In this arrangement, theremaining thin film layer 34 extends across the air bleed slots 38.Strip 50 can be formed by preventing the deposition of the thin film 34in this area during formation, i.e., platting or lithography, or byremoving it after its application. The minimum width of strip 50 isdetermined by the minimum barrier required to prevent problematic crosstalk and depends on the specific parameters of the completed head 46.This embodiment has the advantage of maintaining a large film surfacewhich may be advantageous in minimizing the wear of the surface film andthus increase the lifetime of the head.

Alternatively, elimination of areas of thin film 34 between adjacentchannels is advantageous in that it eliminates a high permeability fluxleakage path that limits the flux across the writing gaps. Hence,elimination of the surface film between the channels will provide forthe maximization of magnetic flux flowing uniformly across the writinggaps 36.

Channel 3 is shown devoid of a thin film layer 34 for ease ofillustration. Writing gaps 36 simply illustrate their position, if thinfilm layer 34 were present. Channels 4 and 5 have thin film layer 34applied over them by pattern 52. Here, pattern 52 is contained withinthe air bleed slots 38, while also providing adequate channelseparation. Pattern 52 illustrates that smaller areas of thin film layer34 are sufficient to accomplish the completion of the head 46. FIG. 17illustrates a furtherance of this concept. Specifically, channel 1 showsan approximation of what would be the minimal acceptable amount ofcoverage for thin film layer 34. Here, thin film layer 34 is justsufficient to contact each pole of ferrite column 16A. The amount ofcontact need only be sufficient to allow the generated magnetic flux toenter and pass through thin film layer 34. The width of thin film layer34 is shown to be contained within glass beading 33. This width could bereduced further, however the minimum width must be sufficient to allowfor writing gaps 36. Though such further minimization is possible, it isoptimal to have thin film layer 34 at least equal the width of theferrite poles 16A to assure proper flux transfer and to prevent theexposure of the corners of ferrite column 16A. For purposes ofpatterning the channel width of thin film 34, the relevant edges can bedefined to fall within the width of the glass bond 33. Such exposedcorners will be localized maximums in the magnetic field and will likelyimproperly write the media. Channel 2 is devoid of thin film layer 34(for ease of illustration), while channels 3-5 show other patterns whichare possible. Virtually any size or shaped pattern could be obtained, solong as sufficient channel separation occurs.

Though various patterns are achievable, certain factors will determinewhich patterns are preferable for any given head 46. To illustrate thesefactors it should be understood that the thin film 34 layer serves adual purpose. First, it completes a magnetic circuit by couplingtogether the poles in the ferrite columns (with or without theadditional consideration of channel separation). Second, the thin filmlayer 34 acts as a tape bearing surface as the media is pulled acrossthe recording head 46. As such, the minimum amount of coverage providedis limited by what is acceptable to create the magnetic circuit.Ultimately, the maximum amount could encompass the entire upper surfaceof the recording head 46. In some cases, such maximized coverage isacceptable. As discussed, it is often desirable to avoid any interactionbetween the thin film layer 34 and the air bleed slots 38. Then, themaximum amount of coverage is defined by the distance D (FIG. 17)between the innermost air bleed slots 38.

An additional consideration arises when an edge (E1-E4) of the thin filmlayer 34 is located within the area defined by distance D and the widthof the head 46. Namely, the media will strike or engage that surfaceE1-E4 as it moves across the head 46. This is normally not aconsideration when the thin film 34 covers the entire head 46 becausethe edge of the thin film 34 corresponds with the edge of the head 46and this occurs at the most extreme point of curvature (due to theradiused head 46). When an edge E1-E4 is located closer to the gaps 36located over ceramic member 14, and the media engages this edge atspeed, it may be caused to skip or jump away from the head 46. Thisissue is problematic if it is random and unpredictable and/or if themedia does not reengage the head prior to the writing gaps 36.Obviously, if it skips the writing gaps 36 the media cannot be properlywritten. Therefore, if an edge E1-E4 is to occur, it is preferable thatit occur further from the writing gaps 36 occurring over ceramic member14, as illustrated in channel 5, by edge E4. In this location, ifskipping or jumping occurs, the media has a longer distance to correctitself. This self correction may also be aided by the curvature of thehead 46. Furthermore, the pattern shown by channels 4 and 5 is alsoadvantageous in that a majority of the material transition regions arecovered by the thin film 34, thus preventing them from damaging orinappropriately writing the media. The transition regions include thetransition from ceramic to glass, from glass to ferrite, and fromferrite to ceramic.

To create the various patterns of thin film layer 34, any known methodof generating and defining a thin film can by utilized. For example,larger areas can have a thin film deposited on them and then wet etchingor ion milling can be used to remove sections. Alternatively, the thinfilm may simply be deposited in the specific pattern desired. Suchtechniques are well known and relatively easy to perform.

In operation, magnetic recording head 46 is secured to an appropriatehead mount. Magnetic tape is caused to move over and in contact with thetape bearing surface of the head 46. At the appropriate periodicinterval, electrical current is caused to flow through the coils 44. Asa result, magnetic flux is caused to flow through the back-bar 40,through the ferrite columns 16A-16E, and through the magnetic thin film34 (as the ceramic member 14 minimizes a direct flow from one pole ofthe ferrite column 16A-16E to the other, causing the magnetic flux toshunt through the permeable magnetic film). As the magnetic flux travelsthrough the magnetic thin film 34, it leaks out through the writing gaps36, thus causing magnetic transitions to occur on the surface of themagnetic tape, in the same pattern and configuration as the gaps 36itself.

The above head fabrication process has been described with respect to amagnetic recording head employing a timing based servo pattern. However,the process could be applied equally well to any type of surface filmrecording head.

The present disclosure presents a plurality of elements and conceptswhich work in a synergistic arrangement to arrive at a highly efficientsurface film magnetic recording head. It is to be understood that thesevarious elements and concepts can be effectively utilized alone or inother combinations than disclosed while still remaining within thespirit and scope of the present invention. Namely, using a columned orcombed head member in and of itself produces a higher quality and moreefficient head. Similarly, removing the high reluctance back-gap andreplacing it with one or more magnetically permeable back-bars leads toa better and more efficient surface film recording head. Utilizing boththe combed structure and back-bars produces an optimal head, achievingsynergistic results. Finally, utilizing a specific pattern ofmagnetically permeable thin film to isolate the channels and to act asthe tape bearing surface, can be used alone or in combination with theabove aspects of the present invention to arrive at a superior recordinghead.

Comparing two heads, each wound with two turns of wire and driven by thesame single channel drive circuit, the head pursuant to this invention(FIG. 13) exhibits a current rise time in the 20 nanosecond range whilethe high inductance head made pursuant to the Albrecht et al. patent(FIG. 18) exhibits current rise time in the 50 nanosecond range. Thecorresponding inductances were measured to be about 250 nH and 700 nH,respectively, for the two heads. The shorter rise time correspondsroughly to the L/R time constant of the head as a circuit element. Hencethe low inductance magnetic recording heads of the present invention arecapable of recording timing based signals on media resulting in sharpermagnetic transitions than media written with previously known heads. Asa result, both the heads produced and the media written by those headswill perform significantly better than the prior art heads and the mediaproduced by them. With due consideration to the details of the writecircuitry, one can expect to at least double the bandwidth by the use ofthe low inductance head of the present invention. Even more dramaticresults can be expected with the independently driven, multi-channel lowinductance head, as illustrated in FIG. 12, while taking into accountthe limitations of the multi-channel drive circuitry.

Those skilled in the art will further appreciate that the presentinvention may be embodied in other specific forms without departing fromthe spirit or central attributes thereof. In that the foregoingdescription of the present invention discloses only exemplaryembodiments thereof, it is to be understood that other variations arecontemplated as being within the scope of the present invention.Accordingly, the present invention is not limited in the particularembodiments which have been described in detail therein. Rather,reference should be made to the appended claims as indicative of thescope and content of the present invention.

1-51. (canceled)
 52. A method of writing magnetic media comprising:providing a multi-channel surface film magnetic recording headcomprising: a plurality of magnetically permeable columns, each columnbeing divided into two parts by a substantially magnetically impermeablegap member, the gap member forming a sub-gap on a writing side of thehead; at least one magnetically impermeable barrier, located between andmagnetically isolating the plurality of magnetically permeable columnsfrom one another; and a magnetically permeable thin film layer spanningat least a portion of the sub-gap and magnetically coupling the twoparts of each column, wherein the thin film layer includes writing gapsdefining a pattern; and writing magnetic media by passing the media overthe head.
 53. The method of writing magnetic media of claim 52, whereinthe recording head further comprises: a plurality of magneticallypermeable back-bars, wherein each magnetically permeable column has aback-bar coupled to it and the back-bar bypasses the magneticallyimpermeable gap member at one end of the magnetically permeable column.54. The method of writing magnetic media of claim 52, wherein the thinfilm layer has been removed in portions so as to magnetically isolateeach of the magnetically permeable columns.
 55. A method of causingmagnetic transitions to occur on a surface of magnetic tape media,wherein at least one servo track on the magnetic tape media is formed bycausing magnetic transitions to occur on a surface of the magnetic tapemedia with a surface film magnetic recording head having a pattern, themethod comprising: providing a surface film magnetic recording headcomprising: a magnetically permeable core; a substantially magneticallyimpermeable member dividing the core into two poles and forming asub-gap; at least one magnetically impermeable barrier dividing the coreand the impermeable member into a plurality of channels; and amagnetically permeable thin film coupling the two poles across thesub-gap, wherein the thin film includes writing gaps forming thepattern; and causing magnetic transitions to occur on a surface of themagnetic tape media in at least one servo track on the magnetic media bypassing the media over the head.
 56. The method of causing magnetictransitions to occur on a surface of magnetic tape media of claim 55,wherein a space between each channel is devoid of the thin film, thespace extending over the entire length of the head.
 57. The method ofcausing magnetic transitions to occur on a surface of magnetic tapemedia of claim 55, wherein the pattern is an amplitude-based pattern.58. The method of method of causing magnetic transitions to occur on asurface of magnetic tape media of claim 55, wherein the pattern is antime-based pattern.
 59. The method of causing magnetic transitions tooccur on a surface of magnetic tape media of claim 55, wherein aseparate back-bar is provided for each channel.
 60. The method ofcausing magnetic transitions to occur on a surface of magnetic tapemedia of claim 55, wherein each channel is magnetically isolated. 61.The method of causing magnetic transitions to occur on a surface ofmagnetic tape media of claim 55, wherein the magnetically impermeablebarrier is ceramic.
 62. A method of writing magnetic media comprising:providing a multi-channel surface film magnetic recording head by:forming a sub-gap substrate by bonding a ceramic member between twomagnetically permeable blocks; cutting the substrate to form a pluralityof columns, wherein each column is divided by a portion of the ceramicmember; providing a ceramic block having a plurality of notchescorresponding to the plurality of columns; bonding the columns withinthe notches to form a head member; processing the head member so thatthe head member has alternating sections of the ceramic and the columnswith the column extending therethrough; coupling at least one winding toa first side of the columns; forming writing gaps in a second side ofthe columns; and writing magnetic media by passing the media over thehead.
 63. The method of writing magnetic media of claim 62, wherein thewriting gaps are in an amplitude-based pattern.
 64. The method ofwriting magnetic media of claim 63, wherein the writing gaps are in atime-based pattern.
 65. Magnetic tape media, wherein at least one servotrack on the magnetic tape media is formed by causing magnetictransitions to occur on a surface of the magnetic tape media with amulti-channel surface film magnetic recording head, the recording headcomprising: a plurality of magnetically permeable columns, each columnbeing divided into two parts by a substantially magnetically impermeablegap member, the gap member forming a sub-gap on a writing side of thehead; at least one magnetically impermeable barrier, located between andmagnetically isolating the plurality of magnetically permeable columnsfrom one another; and a magnetically permeable thin film layer spanningat least a portion of the sub-gap and magnetically coupling the twoparts of each column, wherein the thin film layer includes writing gapsdefining a pattern.
 66. The magnetic tape media of claim 65, wherein therecording head further comprises: a plurality of magnetically permeableback-bars, wherein each magnetically permeable column has a back-barcoupled to it and the back-bar bypasses the magnetically impermeable gapmember at one end of the magnetically permeable column.
 67. The magnetictape media of claim 65, wherein the thin film layer has been removed inportions so as to magnetically isolate each of the magneticallypermeable columns.
 68. Magnetic tape media, wherein at least one servotrack on the magnetic tape media is formed by causing magnetictransitions to occur on a surface of the magnetic tape media with asurface film magnetic recording head having a pattern, the recordinghead comprising: a magnetically permeable core; a substantiallymagnetically impermeable member dividing the core into two poles andforming a sub-gap; at least one magnetically impermeable barrierdividing the core and the impermeable member into a plurality ofchannels; and a magnetically permeable thin film coupling the two polesacross the sub-gap, wherein the thin film includes writing gaps formingthe pattern.
 69. The magnetic tape media of claim 68, wherein a spacebetween each channel is devoid of the thin film, the space extendingover the entire length of the head.